Metals of the platinum group and certain alloys



expression hardening metal,

Patented Feb. 5, 1935 PATENT OFFICE 1,990,277 METALS or THE PLATINUM GROUP AND,

Otto Feussner CERTAIN ALLOY and Alfred Jedele, Hanan-on-the- Main, Germany No Drawing. Application June 30, 1933, Serial No. 678,546. In Germany September 13, 1930 13 Claims.

The present-application is in part acontinuation of our copending application 561,986, filed September 10, 1931. The'invention of the present application relates to effecting improvements in the metals platinum, palladium and gold, and certain alloys of these metals, which include all alloys consisting of the said three metals, and

also alloys consisting of two of these metals, and also alloys containing one or more ofthese metals, together with iridium, osmium, rhodium or ruthenium, or mixtures of these, in which the amount of said added material is relatively low, usually not over 5 to and also certain alloys containing one or, more of the first men.- tioned group of metals, together with small amounts of such metals as copper, nickel, silver, cobalt, tungsten, chromium, tantalum, molybdenum or the like, which alloys are in general .rather soft and hence are easily worked mechanically as by milling, boring, turning, rolling or die pressing, and similar mechanical operations.

It is well known that the metalspalladium, platinum and gold are soft and are very easily worked. It has many times been proposed to I make these metals harder bythe addition of the highly expensive materials iridium, osmium, rhodium or ruthenium or mixtures of the same, in amounts up to 5 or 10%. The metals iridium, osmium, rhodium and ruthenium, and mixtures of these, are hereinafter included in the It has also been proposed to add other metals, which may have more or less hardening eifect.

In accordance with the present invention, we preferably do not add the expensivemetals above referred to, although they are capable of produc-.

ing a certain degree of hardness in the alloys.

The amount of the iridium, rhodium, ruthenium or osmium can in some cases be added up to 40% as readily as the principal metals by themselves or alloys consisting wholly of these principal metals. In accordance with the present invention, ,the principal metals namely platinum, palladium,

gold, and alloys consisting of the three or two of these, which of course may also contain small "amounts of other materials (metals) as impurities, constitute the starting material. The

' metal or alloy is first worked into'the proper me;

chanical shape, which may be a dish, or a crucible or a ring or a spinneret, and preferably without adding the expensive metals above mentioned (iridium, rhodium, ruthenium and osmium) and preferably without adding any 5 I substantial amounts of hardening metals. Silver is not to .be regarded as a metal suitable for the hardening processes, for the reason that it does not produce substantial hardening of the principal metal, but for most purposes silver if 10 present in the alloy is not present to the extent of more than or and never more than 40%. Also we preferably do not add copper or nickel, in any considerable amount, since these would act as hardening agents. However we do not exclude the presence of small ,quantities of copper. or nickel, which might be present as impurities in the precious metal.

It is well known that some of the metals platinum, palladium and gold and alloys consisting of twoor more of these are lacking in hardness, 5 and for certain purposes are unsuitable, on account of not possessing suflicient hardness and strength. These metals and some of their alloys have attractive colors and are used in making jewelry, but the jewelry made from these materials alone is, in many cases, objectionably soft so that the same does not last well. Also in some cases the'jewelry does not retain its luster well.

, These metals are'aiso well known to be highly resistant to various chemicals, including strong acids at the boiling point, solutions of alkali metal sulphides and polysulphides, and if the said metals could be given a sufiicient degree of hardness and sufiicient degree of strength, they wouldbe rendered more'suitable for certain purposes in the chemical industries.

The present invention is based upon our observation that it is possible to form an article out of platinum, palladium or gold or alloys consisting essentially of these, and to carry out the mechanical treating operations such as turning, milling, boring, die pressing, drawing, bending, and the like, during the manufacture of the artich, and then, when the mechanical work has ad antageous to apply the said metalloid hardening agent, in elemental condition, or as a nonoxidized compound, mixed with carbonaceous material such as charcoal or coal, and in a reducing (rather than oxidizing) atmosphere, al-

though in many cases it could be appliedas a vapor (non-oxidized) in an atmosphere of some inert gas. r

Boron appears to give more satisfactory hardening results than silicon, but the latter can also be used in many cases.

We give the following examples, but it is'to be' understood that the invention is not restricted to these examples Example 1 A spinneret, for use in the artificial silk industry is manufactured from pure platinum. The

platinurn'being a soft metal and easily worked, and very malleable and very easily rolled,

stamped, pressed, and bored, the manufacture of the platinum spinneret produces no technical difiiculties. The platinum spinneret (having the minute holes bored therein) is thenpainted on one or both sides with a paste containing charcoal 12 parts, boron 3 parts, diphenyl 1 part and propyl alcohol 6 parts. The coating applied to the said spinneret may be about 1 to 2 millimeters thick, more-or less. The coated article is then wrapped up in copper foil, in order to exclude the atmosphere, and is then heated to a bustible gas may pass through the mufile. At any event care must be taken not to oxidize the coating material. If the heating is conducted in an atmosphere which is devoid of free oxygen, which constitutes the preferred condition, it is immaterial whether the temperature is constant or fluctuates more or less. If on the contrary the atmosphere of the muille contains free oxygen (even in small amount), then it is very advisable not to allow the temperature to fiuctuate ve y' much because such a condition would be likely to give an oxidizing atmos hpere within the copper foil wrapping (at times)", which would cause burning (oxidation) of the boron.

The muflle is well closed and it is advisable to pass a reducing gas through the same, for example fuel gas, particularly during the cooling operation.

The article is thenallowed to cool, without-removing it from the muflle, or from the copper foil wrapping, the cooling being preferably under strongly reducing conditions, and

whenthe'device is cold, or has cooled sufilciently' so that it can be readily handled, it is removed from the muflle. The copper foilmay befound' to be somewhat discolored from the heat, but it should not be thoroughly oxidized, or unsatisfactory results will probably be produced. The copper foil wrapper is taken off, andthe residue of-the paste is brushed off, (and can be used for I making up the next batch of paste, moreof the boron being added thereto).

. neret will then be subjected to polishing in the.

' 1y hardened.

The treated spinusual manner, and will be found to be very great- We have referred above to using a thin copper foil for wrapping the coated article during the heat treatment. Other metal foils which are stable at the temperatures encountered can be 8 3Gb solder.

so long as they are inert with respect to the boron, silicon and carbon.

The hardness of the finished article in this particular case, may-be far above 250 kilograms per square millimeter (Brinell hardness). The elasticity may be about equal to that of a good grade of steel, and the tensile strength may be about equal to that of medium quality of steel.

An alloy of platinum and palladium, containing 98% of platinum and 2% of palladium, or various alloys containing platinum and palladium,

up to 20% of the latter, can be likewise used for the preparation of spinnerets, by the procedure as given above.

If it is desired to harden the material less, in the case of platinum .or the above mentioned platinum-palladium alloys, a temperature of say,

peratures down to about 815 to 825 0., with platie num or palladium above.

The above example can be further modified by alloys of platinum, as given using alloys of platinum, palladium and silver.

Platinum-copper alloys can be'similarly hardened, such alloys being'highly suitable for use in jewelry, to produce alloys having about the same hardness as iridium, which alloyswould cost only a fraction as much as iridium.

In some cases it is possible to omit the prowl alcohol and the diphenylfrom the above mixture and to carry on the heating in an atmosphere of hydrogen, producing very satisfactory results.

Instead of wrapping the article in copper foil, after applying the coating, the article can be embedded in a powdery mixture of boron, carbon and diphenyl, and placed in a nickel-chromium alloy box having a tight-fitting cover, and heated as above indicated. Here also it is advisable to .conduct theheating operation in a somewhat reducing atmosphere, rather than an oxidizing atmosphere. v g

It is possible to use the powder (carbon and boron) four or five times, if care is taken, before it has lost most of its boron. If desired it can be used over many times, by adding a small amount of boron after each use or after each' two or three uses, depending upon the careexer'cised to prevent oxidizing gases coming in contact with the powder at a; high temperature.

For platinum tooth alloy 1. e. alloys suitable for dental purposes such as movable bridges etc. consisting of 40% Pd+50% A8+6% Au+4% Sn or of $0% Pd+36% A8+l0% Au 4% Co+10% Cu-a temperature of 925 0., maintained for about '15 to 80 minutes has been found to be very satisfactoryfor producing the hardening. A temperature fluctuation upto about50 C. ispermissible. v

The above alloys can. also I be hardened some- .what byheatingfor about 45 minutes up to temtemperature' of the The solder should have a melting point of at least 950 C. and preferably substantially over this. It is inadvisable toheat to within about 100 of the melting point of the solder; since the latter may soften somewhat to allow distortion of the article.

Reference was made above to cooling the metal or metal alloy article after the heat treatment. It is advisable to allow the furnace to cool off slowly, rather than to quench the hot articles. For removing'the uncombined residue of hardening substance, some of which may, after the brushing above referred to, cling to the surface of'the hardened article, it is advantageous to brush the article with a little hydrochloric acid or with an aqueous potassium permanganate solution. A solution of sodium peroxide in caustic potash is extremely good for washing-the said article. The article can then be polished (in well known manner) and is ready for use. Prior to the initial heating operation (or coating oper-.- ation) it is advisable to thoroughly cleanse the article, to remove grease, and the like, remaining from various mechanical operations.

- It may be noted that after the hardening operation, the article can be subsequently heated for a long time up to glowing temperatures, without any appreciable diminution of the hardness of the alloy. If the said heating were at a higher temperature and under conditions to permit the oxidation of the boron, the latter would be oxidized and the article would thereby be softened,

' after along time.

In addition to the metalloids boron and silicon, it is also possible to use zirconium metal, in a very finely divided'condition, with the production of satisfactory results.

If desired, treatment of the articles with silicon can be carried out in accordance with the above examples, the temperatures being 800 C. when using a powder of 5 parts of silicon mixed with one part of charcoal. The best time was found to be one hour, when using hydrogen as deoxidizing. gas at a temperature of 50 to 75 C. lower than the temperature above referred to for using boron.

Instead of applying the boron or other element as above described, in the form of a paste, it is also possible to fume the surface of the article with boron, in a reducing atmosphere. It would also be possible to heat the article i1i anatmosphere composed of hydrogen and hydride of boron.

v The silicon can also be applied in the form of vapors of silicon chloride orsilicic chloroform (SiCl4 or SiHCla) These compounds, in the vaper form will decompose at temperatures around meter (according to Brinell) and after treat- 7 nickel alloys (all containing not over 10 to 20% of nickel, for best results).

A particularly useful alloy for some purposes is palladium and 10% gold. This has an initial hardness of 50 kilograms per square milliment of this material by elementary silicon deposited upon the said palladium-gold alloy and subsequently heated to about 800 C., for about 45 minutes, and cooled (all under reducing conditions) the alloy was found to have increased in hardness about tenfold,the said material course being shaped before the treatment-with silicon.

For jewelry purposes silicon is found to be a very suitable hardening metal for an alloy consisting of 96% Pt and 4% expensive platinum metals at a temperatureas mentioned above. The hardness thereby reaches values of platinum with 25% iridium.

In applying this silicon to gold rings for jewelry purposes the best results were found at a temperature of 700C. during 45 minutes. The hardness thereby reached valuss of 150 kg. per square millimeter.-

The dental industry is using palladium with 3 to 20% of other platinum metals, gold or silver as a material suitable for movable bridges or 'the like. In this case it is'recommended to use propyl alcohol other organic compounds can be used which decompose at about 500 C. into hy-' drogen and soot in order to remove theoxygen. For instance: CcHs benzol, CeH4(CH) 2C6H4 anthracene, -(CH3)2C6H4 xylol, CcHsCHs toluol or the like. Also the absorptive qualities of the charcoal in the above mentioned hardening powder can be used. If the charcoal is heated to about 500 C. in ammonia atmosphere and cooled down ammonia is absorbed in large quantities. If this charcoal is mixed with the boron in the above mentioned proportion a powder is obtained with which excellent results in the hardening process were reached without any further organic compounds and'without forming any annoying soot.

The hardening powder with the absorbed ammonia is particularly recommended in using zirconium in the above mentioned powder in the place of silicon. In this case-the hardening temperature should be 50.to C. higher than using boron.

The silicon, boron and the article through its surface, perhaps by a process of diffusion, and the depth of the said diffusion like enter the metal into the body of the metal will depend upon the amount of time and temperature of the heating operation. With shaped articles, having a thickness not over 5 millimeters, the times as stated above, are sumcient to cause diffusion of the hardening agent substantially to the core, and with articles of a much greater thickness, a longer period would be necessary. It is'not necessary however (in most cases) that the heating should be continued until the whole material is uniform'in composition, since if the surface portion of the article is hardened, the article itself is thereby strengthened, even if the material still contains. a core of the soft metal in an unhardened or partly hardened state.

The amount of boron, silicon or zirconium to be taken up by the metal of the platinum-palladium-gold group, will-depend upon the desired liesults. When an amount of silicon or boron equal to -1 or 2% of .the platinum group metal has been absorbed, there is a very considerable hardening produced. In some cases the amount of the V consisting of boron, silicon and zirconium, into have not substantially altered in appearance, in

other words the color and appearance of the platinum metal is substantially the same as before treatment. This is also true of palladium and 801d.

In many cases, a large number of the articles to be hardened can be packed into the powdery composition as above referred to, composedof carbon and silicon or boron, with or without diphenyl or similar reducing agent, in a graphite crucible, which is covered and then put into a furnace and heated tothe temperatures as indicated above.

For many purposes the platinum group metal can be hardened, for instance'a body made of an alloy of 96% platinum and 4% palladium can be hardened by the process above described, to produce a body having a hardness corresponding approximately with that 'oian alloy of 80% platinum and' iridium,'which alloy is also highly chemically resistant and very strong and With regard to the use of the expensive metals osmium, iridium, rhodium'and ruthenium, the distribution of a small percentage (2 to,20%) of any one or more of these in the platinumpalladium-gold metal or alloy consisting of these, causes some hardening. The alloys so formed can then be mechanically worked, and then treated with the boron, silicon or zirconium, producing a further hardening. Except where a very great hardness-is desired, we do not recommend the use of these expensive metals.

We claim:, i

- 1, A process for the production of a shaped obiect with technically valuable'properties from a metalselected from the herein described group consisting of platinum, palladium and gold, and alloys consisting in major part at least of these, which comprises mechanically working thesaid metal to approximately the size and shape of the finished article, and diffusing anon-oxidized substance selected from the herein described group said shaped article, at a glowing heat.

2. A process of producing a shaped object with technically useful properties, of an alloy of a metal selected from the herein described group consisting of platinum, palladium and gold. and alloys consisting in major part at least of these, which comprises first forming a shaped article ol! said metal, which metal is substantially softer than the finished article desired, applying to the surface of said article a layer of an alloy-forming constituent'which can exercise a hardening action 'onsaid metal, said alloy-forming constituent being selected from the group consisting of elemental boron and elemental silicon and volatile non-oxidized compounds of these elements, and thereafter heating the entire under non-oxidizing conditions, sufliclently to cause diiiusion of said surface layer into the v and gold, and alloys consisting in major part at least of these, said heating being in a non-oxi-' dizing atmosphere, while in a material comprising carbon and a non-oxidized hardening agent selected from the herein described group consisting of boron, silicon and zirconium, and continuing, said heating operation until said piece has been hardened to a substantial extent.

4. Process as in claim 3, in which the'platinumpalladium gold group metal is initially given an moderate degree of hardness by alloying a hardening metal therewith, said hardening metal being selected from the group consisting of osmium, iridium, rhodium and ruthenium.

5. A process for the production of a shaped object with technically valuable properties from ametal of the herein described group consisting oiplatinum, palladium, gold and alloys consisting substantially of these, which consists in 'mak-' ing the shaped object of pure metalof the said group which is softer than the finished article desired and diffusing uniformly by heat into the layer of material containing an alloy-forming constituentin a non-oxidized condition; said constituent being selected from the herein described group consisting of silicon and boron, which can .exercise a hardening action'on said alloy, and

thereafter heating the entire body under nonoxidizing conditions sufllciently to cause diffusion of said alloy-forming constituent into the body of said metal alloy, in a minutely sub-divided condition. s

'l. A process which comprises coating ashaped article consisting principally of metal of the herein described group consisting of platinum, palladium, gold, and alloys composed of two at least of said metals, with a composition'comprising an element of the group silicon and boron in nonoxidized state, carbon, a diilicultly volatile 'reducing agent andan alcohol, heating said body up to about 800-900 C. while excluding air therefrom. r

8. A process as in claim '1, in ,which the composition is applied as a paste of the silicon-boron group element, carbon, diphenyl and a higher alcohol.

v 9. Process as in claim 7, in which exclusion :of air is assisted by wrappingthe coated article in a thin metal foil. 7 i

10. A process which comprises forming aspinneret out of a platinum metal, in which the actual platinum constitutes at least 80%, heating said shaped spinneret while in clme contact with an element selected from the herein described group consisting of boron and silicon, to about 800-900 C., under non-oxidizing conditions, until a substantial amount of hardening is effected.

11. A process which comprises heating a shaped piece of a metal selected from the herein described group consisting of platinum, palladium and gold, and alloys, consisting in major part at least of these, said heating being in a non-oxidizing atmosphere, while in a material comprising carbon and a non-oxidized'hzirdening agent selected from the herein described group consisting oxidized condition, hydride of boron, silicon chloride, silicic chloroform; and zirconium, and continuing said heating operation until said piece has been hardened to a substantial extent.

12. A process for the production of a shaped object with technically valuable properties from a metal of the herein described group consisting of platinum, palladium, gold and alloys consisting substantially of these, which consists in making the shaped object of pure metal of the said group which is softer than the finished article desired and diffusing uniformly by heat into the entire body of such metal very finely sub-divided nonmetallic improving agent selected from the herein described group consisting of boron, silicon and non-oxidized compounds of these elements, and zirconium. I

agent selected from the herein described group consisting of silicon, boron, and non-oxidized compounds of these elements which are capable of liberating one of said elements at an elevated temperature, while maintaining same under nonoxidizing conditions, until a substantial amount of hardening is effected. 

